Changes during Firing

The initial mix of the constituents used to form whiteware compositions is composed of relatively large quartz and feldspar grains in a fine-grained clay matrix. 

The clay phase initially shrinks, and fissures frequently appear. Fine mullite needles appear at about 1000°C but cannot be resolved with an optical microscope until temperatures of at least 1250°C are reached. With further increases of temperature, the mullite crystals continue to grow. After firing at temperatures above 1400°C, mullite is present as prismatic crystals up to about 0.01 mm in length. 

No change is observed in the quartz phase until temperatures of about 1250°C are reached. The rounding of edges can then be noticed in small particles. The solution rim of high-silica quartz around each quartz grain increases in amount at higher temperatures. By 1350°C, grains smaller than 20 p are completely dissolved. At above 1400°C, little quartz remains. 

Photomicrographs of electrical insulator porcelain (etched 10 s, 0°C, 4% HF) showing liquid quartz grains with solution rim, feldspar relics with indistinct mullite, unresolved clay matrix, and dark pores, (a) at lower magnification, (b) at higher magnification. 

---

Figure 11. Mineralogical changes during firing of the marl SD 28 and the volcanic noncalcareous clays SD 47 and SD 48.

Bloom, 1981 Fig. 7). Only the dopaminergic neurons fire without significant changes during all sleep-waking stages (Miller et al., 1983 Trulson Preussler, 1984 Fig. 8). 

During firing in a furnace, the clay is heated to a temperature of 1000 °C. A complicated series of chemical changes take place, new minerals are formed and some of the substances in the clay react to form a type of glass. The material produced at the end of the firing, the ceramic, consists of many minute mineral crystals bonded together with glass. 

The conventional batch technique suffers from a number of limitations. The theoretical Mw/Mn=1.33 for three arm star polymers can only be obtained at constant [monomer]/[inifer] ratio (low conversion). When the polymerization is carried to high conversion, this ratio changes during the polymerization. Thus, in batch polymerizations, broad or multimodal MWDs have often been reported. In addition, the PIBs carried unfired or once-fired endgroups. 

---